Spt5p and prokaryotic NusG are shown to contain a novel 'NGN' domain. The combined NGN and KOW motif regions of Spt5 form the binding domain with Spt4 [1]. Spt5 complexes with Spt4 as a 1:1 heterodimer snf this Spt5-Spt4 complex regulates early transcription elongation by RNA polymerase II and has an imputed role in pre-mRNA processing via its physical association with mRNA capping enzymes. The Schizosaccharomyces pombe core Spt5-Spt4 complex is a heterodimer bearing a trypsin-resistant Spt4-binding domain within the Spt5 subunit [2].

1: Novel domains and orthologues of eukaryotic transcription elongation factors. Ponting CP; Nucleic Acids Res. 2002;30:3643-3652. PMID:12202748

2: Characterization of the Schizosaccharomyces pombe Spt5-Spt4 complex. Schwer B, Schneider S, Pei Y, Aronova A, Shuman S; RNA. 2009; [Epub ahead of print] PMID:19460865